Tree canopy provide an insulation effect, cooling the understory during high macroclimatic temperatures and warming it during low temperatures. However, in regions with seasonal snow cover, tree canopy intercept snowfall, which would reduce the insulating effect of snow. Since understory thermal dynamics are crucial for seedling performance, it is important to understand how tree canopy influence the effects of decreased snow cover. We conducted a two-year snow removal experiment in a Picea glehnii forest, comparing conditions under tree canopy and in canopy gap. Four dominant tree species were planted in manipulation plots, and seedling survival and growth were recorded. Air and soil temperatures were continuously monitored. Our findings showed lower air temperatures and more frequent freeze events under the canopy than in gap during snow cover establishment and snowmelt. Snow removal exacerbated these conditions, creating harsher environments under the canopy. Seedling survival reflected these patterns, showing negative responses to decreased snow cover, with certain species exhibiting greater negative responses under the tree canopy. For growth, conifer species had significantly lower rates in snow removal plots. Overall, these results suggest that tree canopy may not protect understory vegetation during dormant seasons in snowy regions. Furthermore, the performances of conifer seedlings in response to snow removal align with the ongoing shift from boreal conifer forests to temperate broadleaf forests in this region. These findings underscore the importance of integrating vegetation-induced microclimate and snow dynamics into forest management strategies, particularly in the context of winter climate change.